During integrated circuit manufacturing, optical inspections of semiconductor wafers (also referred to herein as process limiting yield (PLY) inspections) are performed after each process in the integrated circuit manufacturing line in order to detect defects of interest (DOI) (e.g., critical defects that have the potential to decrease yield). Specifically, during an optical inspection, semiconductor wafers are inspected using a first optical inspection tool in order to capture optical images. The captured optical images are then analyzed to detect defects in inspection care areas (i.e., previously defined areas of interest on the semiconductor wafers), based on a threshold setting for detecting defects. It should be noted that the threshold setting for detecting defects is also referred to herein as the inspection recipe used for detecting defects or the sensitivity threshold for detecting defects. In any case, subsequently, a sample of the inspection care areas is selected (i.e., a smaller representative population of the inspection care areas is selected) and the defects in the inspection care areas in the sample are further inspected using a second optical inspection tool and, particularly, a scanning electron microscope (SEM) in order to capture SEM images. The SEM images of the defects are then analyzed to identify critical defect types (i.e., to classify the defects into different types).
Typically, the first optical inspection tool uses the same threshold setting for detecting defects in all of the different inspection care areas. However, for a given inspection care area, this threshold setting may be either: (a) too low, resulting in overwhelming detection of false defects (e.g., due to wafer or system noise) or nuisance defects (e.g., actual defects identified as non-critical or not affecting yield); or (b) too high, resulting in a failure to detect critical defects. Alternatively, the first optical inspection tool uses different threshold settings for detecting defects in each of the different inspection care areas, respectively. However, determining optimal threshold settings for the different inspection care areas, individually, can be costly in terms of both time and resources. Thus, in deciding how to proceed with the optical inspections, defect engineers in the fab must choose between accuracy and costs.